U.S. Pat. No. 3,906,250 to Sidney Loeb disclosed the basic concept of using liquids of different osmotic pressures to generate power, suggesting that combinations such as seawater and fresh water, or highly saline bodies (such as the Dead Sea) and seawater, as well as other similar pairs of liquids, might be likely candidates for such a renewable energy generation program. This process has now become known as Pressure-Retarded Osmosis (PRO). In the Loeb patent, a number of systems were described that might be used where such natural sources of liquids having two widely different osmotic pressures were unavailable. U.S. Pat. No. 3,978,344 describes such a PRO system where the high pressure, now diluted, high salt concentration liquid was discharged through nozzles to drive turbines.
Since that time there have been a number of U.S. patents issued and articles written describing how PRO systems might be advantageously used as a renewable energy source to generate power, e.g. electrical power, employing naturally available water sources of widely varying salt concentration, or employing the available discharge streams of industrial or municipal installations, such as waste treatment effluents. See, for example, Energy Production at the Dead Sea by Pressure-Retarded Osmosis: Challenge or Chimera by Sidney Loeb, 15 Jul. 1998, Desalination 120 (1998) 247-262; U.S. Pat. No. 6,185,940 B1 issued Feb. 13, 2001 to Prueitt; International Patent Publication No. WO02/13955 A1 published 21 Feb. 2002 to Statkraft SF; and International Patent Publication No. WO2005/017352 A1 published 24 Feb. 2005 to University of Surrey. However, despite the desirability of such proposed systems and despite the fact that large-scale reverse osmosis (RO) facilities for creating fresh water from seawater or saline water sources are in increasingly common use worldwide, such PRO systems have not become commercial. It is believed that the large capital cost involved to build a plant has deterred commercial acceptance of such systems as an alternative to other renewable energy generation sources which have proven track records. As a result, the search has continued for ways to make PRO systems more commercially attractive.